Electrical gas heating apparatus using frequency multiplying circuit and induction blower

ABSTRACT

An electric motor is fed through a frequency multiplying circuit formed by a rectifying circuit with a bypass circuit connected across the motor for removing the DC component of the rectified current so that the motor is fed with an AC current having a higher frequency than that of the supply, the motor being mechanically coupled to drive a gas blower and the bypass circuit comprising a heater in the gas path through the blower.

United States Patent Jones 51 Dec. 5, 1972 [54.] ELECTRICAL GAS HEATING[56] References Cited APPARATUS USING FREQUENCY MULTIPLYING CIRCUIT ANDUNTED STATES PATENTS INDUCTION BLOWER 2,420,213 5/1947 Walker.......321/69 R 3,497,675 2/1970 Yoshiike ..219/364 [72] Inventor. Clive LynnJones, Swansea, Wales 3,575,583 4/1971 Brown I I I "219/364 [73]Assignee: National Research Development 6,963 7/1960 Lee ..321/69 RCorporation, London, England 3,044,004 7/ 1962 Sicard ..321/69 R d: p12, 9 1 3,525,851 8/1970 Seabury, Jr ..219/364 X [21] Appl. M0,; 133,123Primary ExaminerWilliam M. Shoop, Jr.

Attorney -cushman, Darby & Cushman Related US. Application Data [62]Division of Ser. No. 829,920, June 3 1969, Pat. No. [57] ABSTRACT 4 Anelectric motor is fed through 'a frequency multiplying circuit formed bya rectifyingcircuit with a bypass [30] Foreign Application Priority Datacircuit connected across the motor for removing the DC component of therectified current so that the june27,l1996698 great gr tamm, motor isfed with an AC current having a higher an. 1'83 1113111 frequency than.that o the the motor be ng 52] us. Cl. ..219/364, 321/47, 321/69 R andthe I bypass circuit comprising a heater m the gas path [51] Int. Cl..H05b 3/00, F24h 3/04 through the blower [58] Field of Search..219/364; 321/47, 69 R 6 Claims, 23 Drawing Figures PATENTED 5 I97? 3 705,2 9 O SHEET 2 or 9 INVENTOR KO/EJ y/v/v 05/1 55 WORNEYS PAIENTED B 112 3.705.290

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ELECTRICAL GAS HEATING APPARATUS USING FREQUENCY MULTIPLYING CIRCUIT ANDI INDUCTION BLOWER This is a division of my earlier US. application Ser.No. 829,920 filed June 3, 1969 now issued U.S. Pat. No. 3,6ll ,434issued Oct. 5, 1971.

BACKGROUND OF INVENTION A great advantage of cage type or squirrel cageinduction motors over other types of electric motor is their cheapnessand ruggedness, due principally to the absence of any rubbing contactsor insulated windings on the motor.

One limitation of such motors is that the highest speed at which theycan be driven as a motor is, in the case of a single phase two polemotor, approximately equal to the frequency of the alternating voltagesupplied tothe stator windings.

. The main object of the invention is to provide a frequency multiplyingcircuit which may bowed to increase the speed of an induction motorrelative to the supply frequency using relatively simple apparatus.

" SUMMARY OF INVENTION According to one aspect the invention comprises afrequency multiplying electrical circuit including a whole waverectifier circuit adapted to be fed from an A C supply and capacitivelycoupled to a load circuit to feed rectified current thereto, togetherwith a resistive bypass circuit connected to bypass the D C component ofthe rectified current from the load circuit and the arrangement beingsuch that the frequency of the output from the rectifier circuit is amultiple of the input.

According to another aspect the invention comprises a polyphaserectifier circuit adapted to be fed from a polyphase supply and havingthe outputs connected in parallel to a single phase load so that theload is fed from the individual phase circuits sequentially, togetherwith a resistive bypassj circuit connected across the load to bypasstheD C component of the rectified currents.

In applying the invention to an induction motor the induction motorstator will constitute the load.

It will be appreciated that in the case of a single phasesupply using awhole wave rectifier the frequency of the A C voltage fed to the loadwill be double the frequency of the A C supply to the rectifier.

In the case of a three-phase supply the frequency of the voltage fed tothe load will be three times the frequency of the A C supply usinghalf-wave phase rectifiers or using full-wave rectifiers, the voltagefed to the load will be at six times the frequency of the A C supply.

Preferably the rectifiers are solid state rectifiers.

Preferably the bypass circuit has a high inductance so as to block the AC component of the rectified current. The bypass circuit must, ofcourse, be resistive and capable of dissipating the energy of the D Ccomponent of the current output from the rectifier.

According to a further feature the control apparatus is arranged to varythe frequency of the output current. In cases in which the supply feedsan induction motor such control apparatus provides a speed control forthe motor.

According to one embodiment switching apparatus is provided whereby thewhole wave rectifier circuit may be converted at will to a half-waverectifier circuit so as to halve the frequency of the A C output. Such acontrol would of course enable a motor to be run at half speed.

According to another embodiment means are provided for varying theproportions of current which flow through the load and the bypasscircuit. Such a control may be provided by a variable resistance inseries with the load or alternatively in series with the bypass circuit,if desired the bypass circuit may consist of a variable resistance. Inother cases variable resistances may be provided both in the loadcircuit and also in the bypass circuit and these may be ganged.

In the case of a polyphase circuit switching means may be provided forconverting a polyphase circuit to a single phase circuit.

An important application of the invention is in fan heaters, such forexample as hair driers in which the energy of the D C component can beusefully dissipated in the heater. I

In order that the invention maybe more clearly understood reference willnow be made to the accompanying drawings, in which:

FIG. I shows a well-known single phase bridge rectifier.

FIG. 2 shows graphically the currents arising in the rectifier of FIG.1.

. FIG. 3 shows a single phase induction motorfed through a frequencymultiplying circuit embodying the invention. 7

FIG. 4 shows an alternative arrangement to that shown in FIG. 3.

FIG. 5 shows amotor as fed from a three phase supply.

FIG. 6 shows the three-phase circuit of FIG. 5

modified to double the frequency, i. e., to give an outputfrequency sixtimes the frequency of the supply.

FIG. 7 shows the frequency changing supply circuit which corresponds toFIG. 3 but modified to provide two alternative frequencies.

FIG. 8 shows the voltage waveform obtainable with FIG. 7.

FIG. 9 shows an alternative arrangement to FIG. 7.

FIG. 10 shows another arrangementusing a two pole switch.

FIG. 11 corresponds to FIG. 4 modified to provide two outputfrequencies.

FIG. 12 shows FIG. 4 modified to provide a variable input voltage andhence a continuous variation of speed of an induction motor.

FIG. 13 shows how the speed of an induction motor may be varied byvarying the proportions of current passing through the motor and bypasscircuit.

FIG. 14 shows an arrangement alternative to FIG. 13.

FIG. 15 shows an arrangement for switching a three phase half-waverectifying circuit from three phase to single phase.

FIG. 16 shows a corresponding switching arrangement for a three-phasewhole wave rectifying circuit.

FIG. 1l 7 shows a circuit for switching a three phase whole waverectifying circuit to three-phase half-wave, and

FIG. 18 shows an arrangement for switching a threephase whole waverectifying circuit to a single phase half-wave circuit.

FIG. 19 shows an arrangement in which a threephase supply is fed to athree-phase load.

FIG. shows the arrangement of FIG. '19 in which the load is deltaconnected,and

FIG. 21 shows an alternative arrangement in which the load is starconnected.

FIG. 22 is an explanatory view showing how the invention can be appliedto a fan heater using a single phase A C driving motor, and

FIG. 23 is a similar view but showing an arrangement in which the fanheater is driven by a three-phase A C motor.

FIG. 1 shows a well known bridge rectifier circuit comprising fourrectifiers D1, D2, D3 and D4, the A C input is applied across thejunctions between the rectifiers D4 and D1 and the junction between therectifiers D3 and D2.

The D C output is taken from the junction between D3 and D4 and thejunction between D1 and D2.

9 Referring now to the graphs shown in FIG. 2, waveform Sis the A Csupply to the bridge rectifier. Waveform B is the output from thebridge'rectifier. This may be shown to comprise a D C component and an AC component. The D C component C is shown in the third graph whilst thelast graph shows how the A C component D may be obtained by subtractingthe waveform C from the waveform B. It will clearly be seen that thewaveform D is double the frequency of the supply waveform A.

FIG. 3 shows how this rectifier circuit may be used to double thefrequency fed to a motor M. In this case the induction motor M is fedfrom the output of the rectifier circuit through a capacitive couplingC1 whilst a bypass circuit R removes the D C component from the currentfed to the motor M. It will readily be seen that with this arrangementthe motor M is fed with A C at a frequency-double that of the A C supplyfed to the bridge rectifier. By such an arrangement it is possible todesign the motor to run at speeds twice the frequency of the A C supply,assuming of course that themotor winding has a single pair of poles andthat suitable starting arrangements, well known in the art, areprovided.

FIG. 4 shows an alternative arrangement to the bridge rectifier of FIG.3 in which the single phase A C supply is fed through a transformer Thaving a centertapped secondary winding feeding a bi-phase rectifierformed by the individual rectifiers D5 and D6 L being the bypass circuitfor the D C component.

FIG. 5 shows an induction motor fed from a threephase supply. In thisarrangement each of the threephase lines A, B, C is fed to one side ofthe motor through a respective half-wave rectifier D7, D8 and D9 and acommon condenser C1, whilst the other side of the motor is connected toa common neutral line N.

FIG. 6 shows a modification of the arrangement of FIG. 5 in which thephase lines are fed through whole wave rectifiers and the common neutralline is dispensed with. Thus the rectifiers D7, D8 and D9 are connectedto the upper side of the motor winding M through a capacitor C1 whilstthe rectifiers D10, D11 and D12 are connected to the lower side of themotor winding M. Such arrangements enable the motor to be driven at sixtimes the frequency of the A C supply, as-

It will readily be appreciated that the arrangements above shown providea simple and cheap method of increasing the speed of a motor and theinvention has numerous applications in small motor drives where the costof the heat dissipated in the bypass resistor is negligible, forexample, in fan heaters, hair driers and the like. lnthe case of fanheaters the heat dissipated in the bypass circuit may be usefullyemployed for heating purposes.

In some cases the rectifiers may be controlled rectifiers, e.g.,thyristors, which could be arranged to provide a degree of speedcontrol.

It is also possible to cascade the rectifier circuits but in such a casethe current output would be considerably reduced and hence would only beuseful for quite small load currents.

FIG. 7 shows an arrangement corresponding to FIG. 3 but with theaddition of the switch S1. When the switch S1 is closed the circuitoperates normally as a whole wave rectifying circuit and the outputfrequency is double the input frequency. When, however, the

switch 81' is opened the circuit becomes a half-wave rectifying circuitand the output frequency is the same as the input frequency as showngraphically in FIG. 8.

FIG. 9 shows an alternative arrangement in which a two-way switch S2 andan additional rectifier are added. In the position shown, with theswitch moved to its upper position, the upper end of the by-pass circuitR is connected to the junction of D1 and D4 and the circuit acts as ahalf-wave rectifier, with the input and output frequencies the same.When the switch S2 is moved over to the lower position however, thecircuit reverts to its normal full-wave rectifying state and the outputfrequency is double the input frequency. It will be noted that in thefirst position the only operative rectifiers are D5 and D3 in series.

FIG. 10 shows a modification of the arrangement of FIG. 9 in whichsecond two-way switch S3 is added; this switch is ganged with S2 andcuts out the rectifier D3 in the half-wave position so that only therectifier D5 is operative.

FIG. 11 shows FIG. 5 modified by the addition of a switch S4. When theswitch S4 is closed the circuit operates normally to give frequencydoubling, but when the switch S4 is opened the output frequency is thesame as the input.

FIG. 12 shows the arrangement of FIG. 3 in which a variable resistanceVRl is inserted in the input circuit. Such an arrangement can be usedfor varying the speed of an induction motor fed by the circuit.

FIG. 13 shows a modification of the same Figure in which the bypasscircuit is formed by a variable resistance VR2, this permits control ofthe proportion of current flowing through the bypass circuit and controlof the speed of an induction motor.

FIG. 14 shows an alternative arrangement to FIG. 13 in which a variableresistance VR3 is inserted in the motor circuit in place of the variableresistance VR2.

Clearly the arrangements of FIGS. 13 and 14 could be combined and bothresistances VR2 and VR3 employed in which case the two variableresistances would be ganged.

FIG. 15 corresponds to FIG. 5 and shows a threephase half-wave rectifierarrangement in which ganged switches S5 and D6 are added. When theswitches are closed the circuit acts normally and all three phases areoperative; when, however, the switches are opened, phases B and C arecut out and the circuit acts as a single phase circuit. In the case ofan induction motor this will give a speed reduction to one-third of theprevious speed.

FIG. 16 corresponds to FIG. 6 with the addition of the switch S7, whenthe switch is closed the circuit acts normally, i.e., as a three-phasewhole wave rectifier giving a frequency multiplication of six.times,when the switch S7 is opened the circuit changes to a single phase wholewave rectifier, giving a frequency multiplication of four.

.FIG. 17 shows an alternative arrangement to FIG. 16 in which the switchS7 is replaced by the switch S8 in theneutral line. When this switch isin the upper position the circuit acts normally, i.e., as a three-phasewhole wave rectifier, when the switch is in the lower position thecircuit acts as a single phase half-wave rectifier with a frequencyon-sixth of that obtained with the former arrangement.

FIG. 18 shows another arrangement in which two ganged switchs S9 and S10are employed; this produces the same result, i.e., with the switches inthe closed position the circuit acts normally as a three-phase wholewave rectifier with a frequency multiplication of six, with theswitch inthe open position; however, the circuit acts as. a single phasehalf-wave rectifiercircuit, with the output frequency the same as thefrequency of the supply.

It will be appreciated that the variable resistances shown in FIGS. 12,13 and 14 may be used'in any of the other arrangements employingswitching to give additional speed control in the case of the circuitsupplying an induction motor.

FIG. 19 shows a further arrangement in which a three-phase supply is fedto a three-phase load shown as the stator of a squirrel cage inductionmotor. Each individual phase circuit includes a whole wave rectifier andresistive bypass circuit, arranged as shown in FIG.

' Switching to vary the speed can be included, for instance, -inaccordance with the arrangements shown in FIGS. 7 or 9, the switches forthe phases being ganged.

FIG. 20 shows a modification of the arrangement of FIG. 19 in which theload is delta connected, a neutral line is not required in thisarrangement, and

FIG. 21 shows the alternative arrangement in which the load is starconnected, a neutral line being employed with this arrangement.

As mentioned above the invention is applicable to fan heaters and FIG.22 shows an example of such an arrangement in which a rectifier circuitBR, which may be any one of the single phase bridge rectifiers shown inearlier figures or the three-phase arrangement of FIG. 5, feeds a singlephase motor M mechanically coupled to drive a fan blower F, located in agas supply duct D.

The output from the rectifier circuit is connected both to the motor andalso to a heater H which constitutes the bypass circuit above described,and which is located in the duct D so as to heat the gas passing throughit. In this way the heat developed in the bypass heater H is usefullydissipated.

In some cases additional heat may be required and in such cases anadditional heater H, heated directly from the supply may be provided inthe duct.

FIG. 23 shows a corresponding arrangement using a three-phase motor, inthis arrangement the rectifier circuit BR could be any of thethree-phase circuits above described.

In this arrangement three heaters I-Il, H2 and H3 are shown, these actas bypass circuits from the respective phases. The heaters are shownconnected in star, they could of course be connected in delta or thephases kept in separate circuits.

As in the arrangement of FIG. 22 an additional heater I-I fed directlyfrom the mains may be provided if additional heat is required. Clearlythe circuits could be modified for six phases if required.

Apparatus such as shown in FIGS. 22 and 23 may be used for a variety ofpurposes, for example in space heaters for industrial or domesticheating systems, in fan hair driers and clothes driers and in otherapplications in which a fiow of heated gas is required.

I claim: IL A frequencymultiplying circuit in combination with anelectrical inductionmotor and gas heating apparatus comprising: I

a whole wave rectifier circuit arranged to be fed from a polyphasealternating current supply,

a load circuit comprising a polyphase cage type induction motor,

capacitive A C coupling means connected between outputs of the rectifiercircuitand corresponding phases of the 'motor stator winding of theload, I

at least one resistive bypass circuit comprising electric heatersconnected across the corresponding output phases of the rectifiercircuit to bypass the direct current components of the rectified currentfrom the load, and

a gas blow device mechanically connected to the motor to be driventhereby and disposed to cause a gas flow through said electric heatersthereby providing a flow of heated gas.

2. A frequency multiplying circuit in combination with an electricalinduction motor and gas heating apparatus comprising:

a whole wave polyphase rectifier circuit arranged to be fed from apolyphase alternating current electric supply,

a load circuit comprising a polyphase cage type induction motor,

capacitive A C coupling means connected between the output of therectifier circuit and the load,

at least one resistive bypass circuit comprising an electric heatermeans connected across the output of the rectifier circuit to bypass thedirect current components of the rectified current away from the load,and

a gas blower device mechanically connected to the motor to be driventhereby,

said electric heater means being disposed in the gas flow through theblower.

3. A frequency multiplying circuit in combination with an electricalinduction motor and gas heating apparatus, said combination comprising:

a rectifier circuit means having an input for connection to analternating current supply and an output for providing rectifiedcurrent,

a load circuit including said induction motor,

capacitive A C coupling means connected between the output of saidrectifier circuit and said motor for passing the alternating currentcomponent of said rectified current to said motor,

at least one resistive bypass circuit connected across the output ofsaid rectified circuit for bypassing the direct current component ofsaid rectified current away from said motor, and

- a fan blower mechanically coupled to said motor for blowing gas,

said resistive bypass circuit including at least one electricalheater'element in the path of the gas flowing through said fan blowerfor heating said gas.

4. Apparatus comprising a frequency multiplying electrical circuit incombination with an electric induction motor and a gas heating device,said apparatus including:

a rectifier circuit adapted to be fed from an A C electric source,

a capacitive A C coupling connected between an output of the rectifiercircuit and the motor for supplying successive half waves of rectified.cur-

rent to the motor so as to feed the motor with an A C current having afrequency which is a multiple of the frequency of the A C electricsource,

a fan blower driven by said motor, and

a heater for the gas flow through said blower, said heater beingelectrically connected across the rectifier circuit output so as to forma bypass Giffcuit around-the motor for the D C component of therectified current.

5. Apparatus as claimed in claim 4 wherein said rectifier circuitcomprises a single phase whole wave rectifier, and

connections are provided between the rectifier and the motor for feedingthe motor with a current having a frequency double the frequency of theA C electric source.

6. Apparatus as claimed in claim 4 wherein;

said rectifier circuit is a polyphase rectifier adapted to be fed from apolyphase A C electric source and said induction motor has a polyphasewinding.

1. A frequency multiplying circuit in combination with an electricalinduction motor and gas heating apparatus comprising: a whole waverectifier circuit arranged to be fed from a polyphase alternatingcurrent supply, a load circuit comprising a polyphase cage typeinduction motor, capacitive A C coupling means connected between outputsof the rectifier circuit and corresponding phases of the motor statorwinding of the load, at least one resistive bypass circuit comprisingelectric heaters connected across the corresponding output phases of therectifier circuit to bypass the direct current components of therectified current from the load, and a gas blow device mechanicallyconnected to the motor to be driven thereby and disposed to cause a gasflow through said electric heaters thereby providing a flow of heatedgas.
 2. A frequency multiplying circuit in combination with anelectrical induction motor and gas heating apparatus comprising: a wholewave polyphase rectifier circuit arranged to be fed from a polyphasealternating current electric supply, a load circuit comprising apolyphase cage type induction motor, capacitive A C coupling meansconnected between the output of the rectifier circuit and the load, atleast one resistive bypass circuit comprising an electric heater meansconnected across the output of the rectifier circuit to bypass thedirect current components of the rectified current away from the load,and a gas blower device mechanically connected to the motor to be driventhereby, said electric heater means being disposed in the gas flowthrough the blower.
 3. A frequency multiplying circuit in combinationwith an electrical induction motor and gas heating apparatus, saidcombination comprising: a rectifier circuit means having an input forconnection to an alternating current supply and an output for providinGrectified current, a load circuit including said induction motor,capacitive A C coupling means connected between the output of saidrectifier circuit and said motor for passing the alternating currentcomponent of said rectified current to said motor, at least oneresistive bypass circuit connected across the output of said rectifiedcircuit for bypassing the direct current component of said rectifiedcurrent away from said motor, and a fan blower mechanically coupled tosaid motor for blowing gas, said resistive bypass circuit including atleast one electrical heater element in the path of the gas flowingthrough said fan blower for heating said gas.
 4. Apparatus comprising afrequency multiplying electrical circuit in combination with an electricinduction motor and a gas heating device, said apparatus including: arectifier circuit adapted to be fed from an A C electric source, acapacitive A C coupling connected between an output of the rectifiercircuit and the motor for supplying successive half waves of rectifiedcurrent to the motor so as to feed the motor with an A C current havinga frequency which is a multiple of the frequency of the A C electricsource, a fan blower driven by said motor, and a heater for the gas flowthrough said blower, said heater being electrically connected across therectifier circuit output so as to form a bypass circuit around the motorfor the D C component of the rectified current.
 5. Apparatus as claimedin claim 4 wherein said rectifier circuit comprises a single phase wholewave rectifier, and connections are provided between the rectifier andthe motor for feeding the motor with a current having a frequency doublethe frequency of the A C electric source.
 6. Apparatus as claimed inclaim 4 wherein; said rectifier circuit is a polyphase rectifier adaptedto be fed from a polyphase A C electric source and said induction motorhas a polyphase winding.